2009 Volume 50 Issue 3 Pages 562-569
The effect of application alternating current on the modification of primary Mg2Si crystals in the hypereutectic Mg-4.8 mass%Si alloy has been investigated in the present study. The liquidus and eutectic temperatures of the Mg-4.8 mass%Si alloy are 761°C and 638°C, respectively. An alternating current of 60 A with frequency of 1 kHz was applied into the hypereutectic Mg-Si melt from different starting temperatures (770, 740, 700 and 670°C) till 630°C. The results show that primary Mg2Si crystals could be refined effectively by application alternating current. The average sizes of primary Mg2Si crystals were decreased to almost a half after being subjected to the alternating current. The starting temperature of the application alternating current is a very significant factor to determine the size uniformity of the primary Mg2Si crystals, while it has no obvious effect on the average size of the primary Mg2Si crystals. The refined primary Mg2Si crystals have the lowest average size and the highest uniformity in sizes when the hypereutectic Mg-Si melt was treated by application alternating current from the starting temperature of 700°C.